1. Field of the Invention
This invention relates to an improved modular screw anchor which is easily installed even under the most difficult of soil conditions and which is designed to considerably reduce manufacturing and inventory costs. More particularly, it is concerned with a two component anchor having an elongated rod component and an anchor member. The elongated rod incorporates an earth penetrating lead at one end, an annular, outwardly extending flange adjacent the lead, and a drive boss adjacent the flange. The anchor member includes an elongated bore-defining hub, an outwardly extending load-bearing element secured to the hub and an apertured plate secured transversely to the hub bore. When the anchor member component and the rod component are assembled in accordance with the present invention, the resulting earth anchor can be installed using conventional screw anchor wrenches and, advantageously, the wrench drivingly engages each component separately.
2. Description of the Prior Art
Power installed earth screw anchors have gained widespread use in a variety of applications. Dominating the power installed earth screw anchor market is an anchor comprising an elongated, square in cross-section shaft having a beveled, earth-penetrating end, and one or more helical blades affixed to the square shaft. For installing such an anchor, a conventional, square in cross-section, tubular anchor wrench is drivingly engaged to the anchor by inserting the square shaft into the wrench tube. The wrench tube is typically operably coupled to power installation equipment, whereby axial rotation of the wrench tube in turn axially rotates the screw anchor, and effects installation of the anchor into the earth. While this anchor and installation method are effective in normal soils, problems have been encountered in installing this type of anchor in many types of soils, such as glacial till, broken rock, gravel, sandstone, limestone, shale, and clay. While modern installation equipment can develop sufficient torque to install the anchor, such an anchor when encountering the difficult soil has a tendency to break apart, either by breaking the anchor shaft or stripping the helical blades from the shaft.
A modular screw anchor has been recently developed which overcomes the torsional breakage problem typical with the conventional screw anchor. An example of this revolutionary modular screw anchor is illustrated on page 2 of the May 1982 issue of Chance Tips published by A. B. Chance Company, Centralia, Mo. Such a modular anchor incorporates a helical screw blade secured to a unitary, open-ended, square in cross-section, tubular hub. The anchor also includes an elongated, unitary, forged rod assembly which includes a beveled lead point at one end, an enlarged circular flange adjacent the lead, and a square in cross-section wrench-engaging portion adjacent the flange. The rod assembly is inserted through the tubular hub until the rod flange contacts the hub walls. A conventional tubular screw anchor wrench is then telescoped over the anchor rod such that the outer faces of the wrench drivingly engage the inner wa11s of the tubular hub, and the inner faces of the wrench drivingly engage the square, wrench-engaging portion of the rod.
This revolutionary modular screw wrench has yielded spectacular results in overcoming many of the torsional breakage problems associated with previous screw anchors. However, the manufacture of this modular screw anchor has proven expensive for several reasons. First, the forging technology for making the wrench engaging section, flange and lead is such that, for practical purposes, only elongated rods of larger diameters can be used. Smaller diameter rods have insufficient material for forging of these components. However, for many applications at the critical regions of the rod, the tensile strength of such a large diameter rod is simply not necessary and thus use of these large rods constitutes a serious and expensive waste of materials. Additionally, it has been discovered to be expensive to manufacture the square, tubular hub because of the bending, holding jigs, and tack welding steps involved. Thus, while the newly developed modular screw anchor is very effective in anchor applications, it can be expensive to manufacture and use, particularly in anchoring applications where relatively small diameter rods are sufficient.